40-year trend study finds signs of improved water quality in New Jersey streams

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A USGS analysis of New Jersey water quality trends found levels of total nitrogen and total phosphorus, which fuel algae blooms, declined or stayed the same at most stream sites between the 1970s and 2011. At all sites studied, chlorides from road salt increased over that time.

The U.S. Geological Survey (USGS) has found significant changes in nutrient levels at many of the 28 New Jersey streams where water quality has been monitored from the 1970’s through 2011. A new USGS analysis finds that across the state, most long-term stream monitoring sites showed either downward trends in levels of nitrogen and phosphorus -  indicating some water quality improvement - or only slight variations in levels of the two nutrients. A subset of sites analyzed for chloride, or salt compounds, showed upward trends.

Map of New Jersey showing water sampling sites
Map credit: USGS (Public domain)

Nutrients such as nitrogen and phosphorus are essential for plant and animal life, and occur naturally in most New Jersey waterways. However, heavy nutrient concentrations in streams can cause increased algal blooms, taste and odor problems in drinking-water supplies, and low levels of dissolved oxygen in the water, which in turn can harm aquatic life. In drinking water, high levels of nitrate, a form of nitrogen in fertilizer, can cause serious health problems for infants. Greater-than-natural levels of nutrients in streams can come from treated wastewater discharges and septic-system drainage, as well as fertilizer runoff from agriculture settings, residential lawns, golf courses, and construction sites.

A network of long-term stream monitoring stations, installed between 1971 and 1978 and sampled by the New Jersey Department of Environmental Protection and the USGS since the mid-1970s, provided most of the data. The stations are jointly funded by the state and USGS and are sampled four times a year. The monitoring stations where data was collected on salinity trends in the Delaware River were funded by NJDEP, USGS and the Delaware River Basin Commission.  

 “The US Geological Survey and the New Jersey DEP have a longstanding and productive partnership,” said Bob Hirsch, a USGS scientist who co-authored the report. “Both agencies fully appreciate the importance residents in the nation’s most densely populated state place on water quality. With this comprehensive data set and newer statistical methods, we were able to provide our broadest assessment yet of nutrient trends of the state.”

Concentrations of phosphorus and of all forms of nitrogen at most of the 28 study sites either decreased or did not change significantly from 1980 through 2011. There was an upward trend in phosphorus at one station and an upward trend in all nitrogen compounds combined at two sites.  There was an upward trend in nitrate identified at nine stations and downward trends at seven sites.  

These results are consistent with those observed in a USGS study of streams in the Northeastern US for a similar time period. In the Northeast study, the increasing nitrate trends in many urban streams were attributed to implementation of wastewater-treatment improvements that convert nitrogen in wastewater discharges to nitrate.

“Modernization of wastewater treatment plants, better stormwater management at the local level, decades of good work by the DEP, and tough laws protecting rivers, streams, and ecologically sensitive areas along them are resulting in healthier waterways,” said New Jersey DEP Commissioner Bob Martin.

Wintry trees and grasses line New Jersey's Mantua Creek.
Trees and grasses provide a natural buffer along the undeveloped banks of New Jersey's Mantua Creek. Photo courtesy of NJ DEP (Public domain)

USGS researchers also examined trends in salinity at four sites in the New Jersey portion of the Delaware River drainage. Upward trends were observed at all four sites, with chloride concentrations nearly doubling over the last 30 years. Other studies in the northeastern US have yielded similar results.

“Increasing trends in chloride concentrations are common in rivers in urban areas across the northern U.S. and appear to be related to increased use of road salt in recent decades. Elevated salt concentrations in streams can harm aquatic organisms” Hirsch said.

To find out whether these trends in water quality have been going on throughout the entire study period or if they are more recent, the researchers did a decade-by-decade analysis of the nutrient levels.  They found that nutrient levels continued to improve throughout the study’s 40-year span. However, the greatest progress was in the first three decades. From 2000 through 2011, fewer locations showed improvements in nutrient levels. Meanwhile, chloride concentrations continued to climb from 2000 to 2011 at all four locations.  These results indicate that water-quality in streams is improving for nutrients, but other stressors need further evaluation. 

The USGS Scientific Investigations Report 2016-5176, Trends in the Quality of Water in New Jersey Streams, Water Years 1971-2011, is available for download at  https://pubs.er.usgs.gov/publication/sir20165176.